1. Field of the Invention
The present invention relates to a 2-dimensional (2D)/3-dimensional (3D) switchable display device, and more particularly, to a 2D-3D switchable display device that can easily convert between displaying 2D and 3D images, can be easily mass-manufactured, and has low power consumption.
2. Description of the Related Art
Recently, 3-dimensional display devices have been used in various fields, such as medical imaging, games, advertisements, education, military applications, etc. Also, many studies have been undertaken to display 3D images using holographic and stereoscopic techniques.
The holographic technique is an ideal technique, but it requires a coherent light source, and thus it is difficult to record and reproduce a large-sized object located at a long distance using this technique. On the other hand, the stereoscopic technique employs a stereoscopic effect caused by a binocular parallax between two 2-dimensional images that are respectively seen by the two eyes of a user. Since the stereoscopic technique is performed using two planar images, 3D images with high resolution and great depth may be displayed in a simple manner. The stereoscopic technique is classified into a glasses-type display technique, which utilizes polarized light and a shutter to allow two eyes to see separate images, and a glassesless-type autostereoscopic display technique, in which a display device directly separates images to form fields of view. In the case of a glassesless-type autostereoscopic display device, the number of viewers is restricted because an observation range is fixed. Nevertheless, the glassesless-type autostereoscopic display device is generally preferred to a display device that requires viewers to wear additional glasses.
The glassesless-type autostereoscopic display device is classified into a parallax barrier type and a lenticular type. The parallax barrier type display realizes a stereoscopic image by separating light in left eye and right eye directions by a barrier in order to form a binocular parallax. Since, in the parallax barrier type display, light is blocked by the barrier, it is almost inevitable that light efficiency decreases. On the other hand, the lenticular type display realizes a stereoscopic image by disposing images corresponding to the left and right eyes on a focal surface of a lenticular lens and separating the images into images corresponding to the left and right eyes according to the directional characteristic of the lenticular lens. That is, since an image is separated into left and right images using all light in the lenticular type display, the lenticular type display is more advantageous than the parallax barrier type display in terms of light efficiency.
FIG. 1 is a view illustrating a conventional 2D-3D display apparatus disclosed in U.S. Pat. No. 6,069,650. The 2D-3D display apparatus includes a lenticular means 15. The lenticular means 15 includes a lenticular sheet 30, a liquid crystal layer 38, and a plate 36. A transparent conductive film 34 is placed between the lenticular sheet 30 and the liquid crystal layer 38. A transparent conductive film 37 is also placed between the liquid crystal layer 38 and the plate 36. The lenticular sheet 30 includes a lenticular element 16. The 2D-3D display apparatus includes a power source 40 for applying power to the liquid crystal layer 38 and a switch 41.
In FIG. 1, when the power source 40 is switched on or off, refraction indexes of the liquid crystal layer 38 and the lenticular sheet 30 are the same or different, respectively. When the refraction index of the liquid crystal layer 38 is the same as that of the lenticular sheet 30, light incident on the lenticular sheet 30 passes through the lenticular sheet 30 and the liquid crystal layer 38 without refraction to form an image in a 2D mode. On the other hand, when the refraction index of the liquid crystal layer 38 is different from that of the lenticular sheet 30, images are separated into left and right images to be displayed by the lenticular sheet 30. Thus, an image in a 3D mode is formed.
Since the lenticular element 16 having a spherical shape is formed on a lower surface of the liquid crystal layer 38, the thickness of the liquid crystal layer 38 increases. Accordingly, since a driving voltage should be increased, power consumption is increased. Also, it is difficult to continuously control the liquid crystal layer 38 having a spherical shape. In addition, since the lenticular means 15 is formed by filling a lens with liquid crystal, which requires a special manufacturing technique, and it is difficult to switch the liquid crystal layer 38, the reliability of the 2D-3D display apparatus is low.